http://en.wikipedia.org/wiki/Diesel-electric_transmission
It sounds to me that what the wikipedia article is saying is that a piston of a combustible engine that is attached to wheel axle (where the engined torque is applied) is stymied by the amount of expansion of the piston. With combustion as the source of the torque, the energy is supplied by a chemical reaction which is under physical constraints (V, T, P) and if say the wheel were stuck, the piston would be stuck so that the combustion chamber was at some volume; that volume might not be ideal for a chemical reaction, all the time.
If the chemical energy is transfered to electrial, the electromagnetic motor as all the energy available, perhaps pre-stored in a battery, and can apply full torque to a stopped wheel without the wheel having any feedback on the amount of energy that the electrical generator applies.
That's how I read it at least.